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Minimum Exit Pupil?

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JAM
JAM's picture
Minimum Exit Pupil?

The visual observing manual mentions (in passing) challenges using less than a 2mm exit pupil, and also indicates E and F chart scales are for large scopes.

I'd intended to use my 4" refractor with exit pupils down to 0.5mm, and E and F charts for fainter variables, particularly at home in brighter skies.  

I don't understand if the above is a hindrance to variable observation (or if the manual indeed implies that). I thoroughly understand the concept of exit pupil/magnification as it relates to contrast/limiting magnitude etc.

I'm keen to submit accurate data, so if any experienced observers see an issue with this I am happy to hear from you.

Thanks,
Andrew

pox
pox's picture
As a general rule the size of

As a general rule the size of the observer's eye pupil decreases with age, from a maximum of (I believe) about 7mm, so for example 7 x 50 binoculars which give this size exit pupil make optimum use of your 'organic detectors' as does any optical system giving a comparable exit pupil. Small EPs present unfortunately a host of attendant problems. I know when I use a high power (not very often if possible) it is physically a challenge to keep the small exit pupil from falling on the centre of my eye pupil.

JAM
JAM's picture
Thanks for your response.

Thanks for your response.

If averted vision with small exit and eye pupils is the main difficulty, that may not apply to me; my eye pupil is 7-8mm. I don't match an exit pupil to that unless I'm optimizing surface brightness for extended objects, or (incidentally) when lowering magnification for bright variables. I love low power views, but not at the expense of a broad selection of fainter targets I could otherwise accurately observe.

Please feel free to let me know if I've missed or misunderstood something, though.

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